• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.5
• /
• pp.1479-1485
• /
• 1991

본 연구에서는 고차판이론(higher order shear deformable plate theory)을 사용하여 DCB시편을 보형상이 아닌 실제의 얇은 판으로 해석하여 새로운 에너지해방률 식을 제시하고자 한다.한편, 이의 타당성을 입증하기 위하여 Gr/Ep 및 APC-2 복합 재료로 ASTM D30.02 round robin의 제안 방법에 의해 층간파괴인성치를 구하고, 또 이 강용이 제안한 Ae법에 의한 금속의 파괴인성치 결정법을 참고로 하여 미세파괴 초창기 의 층간파괴인성치를 결정하여 이론결과와 비교 검토한다.

• Composites Research
• /
• v.21 no.4
• /
• pp.7-14
• /
• 2008

Prediction of the load-bearing capacity of an adhesive-bonded Joint is of practical importance for engineers. This paper introduces interface fracture mechanics approach to predict the load-bearing capacity of composite metal bonded joints. The adhesion strength of composite/steel bonding is evaluated in terms of the energy release rate of an interfacial crack and the fracture toughness of the interface. Virtual track closure technique (VCCT) is used to calculate energy release rates, and hi-material end-notched flexure (ENF) specimens are devised to measure the interfacial fracture toughness. Bi-material ENF specimens gave consistent mode II fracture toughness $(G_{IIc})$ values of the composite/steel interface regardless of the thickness of specimens. The critical energy release rates of double-lap joints showed a good agreement with the measured fracture toughness. Therefore. the energy-based interfacial fracture characterization can be a practical engineering tool for predicting the load-bearing capacity of bonded joints.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2002.10a
• /
• pp.812-815
• /
• 2002

The shape of K-R curve for an ideally brittle material is flat because the surface energy is an unvaried material property. However, the K-R curve can take on a variety of shapes when nonlinear material behavior accompanies fracture. By the way, a general metallic material is nonlinear, structural steel is such. Therefore, the J-R curve form J-integral value instead of K parameters can be used to evaluate elastic-plastic materials with flaws in terms of ductile fracture that can be significant to design. In this paper, R-curve behaviors form K and J parameter is considered for the precise assessment of fracture analysis, in case of JS-SS400 steels.

• Journal of the Korean Society for Precision Engineering
• /
• v.15 no.11
• /
• pp.251-257
• /
• 1998

동적 파괴인성치 측정시스템과 동적 2차원 유한요소해석 프로그램을 개발하여 원자로압력용기에 사용하는 강(SA508 cl.3, SA516 gr.70)의 동적 파괴인성치와 동적 균열정지인성치를 평가하고 이에 대한 유용성을 확인하였으며, 이 시스템 을 이용하여 재료의 동적 파괴특성을 규명하였다. SA508 cl.3와 SA516 gr.70의 동적 균열전파속도(a)에 대응하는 동적 응력확대계수 (K(a))에 대한 실험식을 얻었으며, 동적 응력확대계수와 동적 균열전파속도와의 관계는 전형적인 "$\Gamma$" 형으로 나타남을 확인하였다.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.3
• /
• pp.497-505
• /
• 1992

본 연구에서는 최근에 개발된 직물 탄소섬유강화 복합재료의 파괴인성치를 정 량적으로 결정하고 파괴거동을 조사하고자 한다. 본 연구의 목적은 이 재료에 선형 탄성파괴역학의 적용여부를 알아보고, R곡선을 이용하여 균열의 생성점 및 불안정 파 괴점의 파괴인성치를 정확히 구하며, 주사형 전자현미경을 통해 파단면 및 균열 성장 시점을 관찰하여 파괴거동을 조사하는데 있다.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.11 no.5
• /
• pp.717-724
• /
• 1987

Mechanical properties tests and fracture toughness tests of turbine rotors were performed in the wide range of temperatures, -150.deg.C-+150.deg.C, and fracture toughness values from above tests were compared with the estimated values from mechanical properties at lower and upper shelf temperatures and FATT. The relations between mechanical properties and $K_{IC}$ properties proposed by Rolfe and Begley were reviewed and confirmed through these experimental results. On the fracture surfaces of some specimens which were satisfied with the Ikeda's $K_{IC}$ criterion micro dimple zone was detected at the rear of fatigue crack zone and it was confirmed that these specimens were not satisfied with the thickness requirement of ASTM E 399.E 399.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.10 no.2
• /
• pp.198-207
• /
• 1986

This study investigates interlaminar fracture characteristics of Graphite/Epoxy composite (HFG Graphite/Epoxy) under mode I (opening mode), mode II (sliding mode) and mixed mode loading conditions. The effects on interlaminar fracture toughness due to different fiber orientations on the crack surface are also investigated. The antisymmetric test fixture proposed by M. Arcan is used for this test. Both critical stress intensity foctors and critical energy release rates were determined and several mixed mode fracture criteria were compared to the experimental data. Also fracture surfaces were investigaed to obtain informations on the fracture behaviors of Graphite/Epoxy composite by means of a scanning electron microscope(SEM).

• Journal of the Korean Institute of Gas
• /
• v.1 no.1
• /
• pp.95-100
• /
• 1997

In order to predict the elastic-plastic fracture toughness for metallic materials, Finite Element Method(FEM) was used for analysis of compact tension specimen. ASTM E399 test procedure was adopted for simulation of FEM. The Load-Crack Mouth Opening Displacement curve obtained from this analysis was used to detect the crack initiation point and determine the elastic-plastic fracture toughness $J_{IC}$. In order to prove the results, they were compared with the results from previous experiments and they agree with experimental results.

• Journal of the Society of Naval Architects of Korea
• /
• v.34 no.3
• /
• pp.61-69
• /
• 1997

A simple and relatively new experimental method is proposed to estimate the plane stress fracture toughness by using compact tension (CT) specimen. The anti-buckling plates (fabricated to prevent the buckling caused by the 45 plastic yielding around crack tip under the plane stress condition) help to determine the relatively accurate plane stress fracture toughness of two stainless steels (SS304 and SS316). The fatigue crack propagation behavior of two stainless steels under two different loading conditions such as 10Hz and 5Hz frequency fatigue loadings was investigated by using image analysis technique (IAT) which renders several technical advantages over various conventional measuring methods. It was found that the IAT could be used to estimate fatigue crack lengths more effectively. Furthermore, it was suggested that we might control the measuring time interval for fatigue crack propagation by nearly automatically controlled technical process with the help of IAT.

• Journal of the Korean Society for Precision Engineering
• /
• v.4 no.4
• /
• pp.13-21
• /
• 1987

4-4 품질관리 품질관리에는 세가지의 중요한 스텝이 있다. 첫째는 소요자재의 관리, 두째는 공장에서 조립할때의 관리, 세째는 출고관리이다. 특수 파괴설계방법론을 이 모든 과정들에 적용시켜야 할 것이다. 4-4-1 수입자재의 품질 자재들을 매입 혹은 수입할 경우에 검사하여야 할 여러가지 가 있다. 1 재료를 매입할 때 성질들이 얼마나 균일한가\ulcorner 2 최소 인성치는 얼마로 보증되어 있는가\ulcorner 3 재료들을 선별하여 거절하느나, 수락하느냐를 결정하기 위하여 어떠한 비파괴 검사법을 사용하느나\ulcorner 수입재료들에 대해서 파괴측정 시험을 해보면 실험방법이나 재료종류들에 관련되어서 실험데이타들에 전형적인 산포현상이 나타나게 마련이다. 예를들어보면 항복응력이 1400Mpa인 퀘칭하여 켐퍼링한 강의 공칭 파괴인성치는 $_{4}$는 90Mpa .root. m 일 수도 있고 60Mpa .root. m일 수도 있다. 아래 그림에 이 현상을 예시하였다. 파괴문제가 중요시 되는 부품에 대해서는 특수하게 파괴인성치를 규정하여 재료를 구입하여야 한다.